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Goin’ Underground Fig. 3: Exterior portal leads to 150 ft (45 m) long tunnel and various chambers to create a wine cave 45 ft (14 m) under the owner’s new home Fig. 4: Wet-mix shotcrete was applied 6 in. (150 mm) thick over welded wire reinforcement in four passes Fig. 5: Organic shape is sculpted wet shotcrete, hand-raked and troweled limestone and red clay earth. A skid steer removed the spoils. Dry-mix shotcreting was used for soil stabilization. “Because they would excavate then shotcrete sporadically, they elected to use the dry-mix method because it could be applied on demand without a pump and ready mix truck standing by,” Mitchell explained. The Quikrete product used for dry-mix shotcreting is a specially formulated microsilica-enhanced, portland cement-based, high-strength structural material (refer to Fig. 2). Over the 2 years of excavation and shotcreting by Bacchus Caves, their efforts resulted in the 10 ft (3 m) diameter x 150 ft (46 m) cask storage tunnel, a 17 ft wide x 15 ft tall x 23 ft long (5.2 x 4.6 x 7 m) bottling storage room, an 18 x 15 x 40 ft (5.5 x 4.6 x 12 m) tasting room, a 17 x 15 x 48 ft (5.2 x 4.6 x 15 m) dining room with butler’s pantry, and 10 x 10 x 30 ft (3 x 3 x 9 m) wine library. “The excavation and shotcreting moved pretty slowly because it is clay soil with huge suspended boulders interspersed throughout the area,” Mitchell explained. “They did have a cave-in for an area we were calling the “Grotto,” which was finally abandoned.” The cave has two portals: the outside entrance, and an access point from the basement of the house with a spiral staircase and elevator (refer to Fig. 3). Hundreds of cubic yards of the dry-mix shotcrete were consumed during the process. “Every couple of feet, they would apply a structural coat of shotcrete and then reapply additional coats over previously applied shotcrete as they came back out,” said Mitchell. After excavating and structural shotcreting was completed, 4 x 4 in. (100 x 100 mm) welded wire reinforcement was applied to the entire interior surface and spaced off the walls. The electrical conduits were placed between the two layers of shotcrete. “We placed 6 in. (152 mm) of wet-mix shotcrete for the final tunnel liner, applied in 1.5 in. (38 mm) layers,” Mitchell, who is also the nozzleman, explained. “This would result in about four passes to achieve 6 in. (150 mm) of wet shotcrete applied over as much as 14 in. (350 mm) of dry mix” (refer to Fig. 4). The wet mix sped up the process by spraying at a much higher rate than dry-mix shotcrete. Screed rakes were used to contour the larger radii such as the arches (refer to Fig. 5). Hand trowels were used to knock down any high points. Three color samples were test batched for the owner. Mitchell and co-worker Rich Lederer worked together to create the organic shapes. “Nature drives the design.” Shotcrete • Spring 2016 47


2016SpringShotcreteEMag
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